Causes

Smallpox is caused by infection with the variola virus. The virus can be transmitted:

Directly from person to person. Direct transmission of the virus requires fairly prolonged face-to-face contact. The virus can be transmitted through the air by droplets that escape when an infected person coughs, sneezes or talks.

Indirectly from an infected person. In rare instances, airborne virus can spread farther, possibly through the ventilation system in a building, infecting people in other rooms or on other floors.

Via contaminated items. Smallpox can also spread through contact with contaminated clothing and bedding, although the risk of infection from these sources is less common.

As a terrorist weapon, potentially. A deliberate release of smallpox is a remote threat. However, because any release of the virus could spread the disease quickly, government officials have taken numerous precautions to protect against this possibility, such as stockpiling smallpox vaccine.

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